1. Field of the Invention
This invention relates to a composition and method for preventing the deposition of scale in wells and well drilling equipment used to drill reservoirs containing high temperature aqueous liquids. More particularly the invention relates to such a composition and method for preventing the deposition of scale onto the sidewall of a well and onto metal surfaces from high temperature brines from oil and gas producing wells or geothermal fluids containing calcium or other scale-forming ions when such reservoir fluids contact the drilling fluid and are circulated through the well drilling equipment along with the drilling fluid.
2. Description of the Prior Art
Drilling wells into subterranean reservoirs containing hot aqueous fluids such as brine along with gas and oil or geothermal fluids presents many problems concerning the choice of a drilling fluid. Conventional aqueous base drilling fluid containing water, clay and various additives is generally used in drilling the first two to four thousand feet of hole through the usually somewhat incompetent strata above the reservoir containing high temperature fluids. Casing is cemented in place over this portion of the hole and drilling is continued using any one of a number of drilling fluids. Problems arise at lower depths when the drill bit penetrates those reservoirs containing a high temperature brine or a geothermal fluid, which reservoirs often lie several thousand feet below the surface. Such reservoirs are often highly porous and permeable. If conventional drilling fluid is used, the weight of the high gravity column of drilling fluid in the well is so great that a considerable amount of the fluid invades the reservoir. This necessitates use of a large additional volume of fluid and results in partial plugging of the reservoir by the clay and other solids in the fluid. When the well is subsequently completed, this plugging decreases the amount of formation fluid which can be produced via the well. If a relatively light-weight drilling fluid, such as air or another gas, is used, a high rate of circulation of the drilling fluid through the system is required to circulate cuttings out of the hole. This high rate of circulation of the drilling fluid together with the fluids produced from the reservoir, result in corrosion and erosion problems. The high velocity gaseous fluids erode the unconsolidated portions of the reservoir to such an extent that hole stability cannot be achieved. In many cases, even the drill pipe is eroded.
One solution to these problems has been to drill reservoirs containing a high temperature aqueous fluid with aqueous gas-containing drilling fluid. Use of this light-weight, gas-containing drilling fluid comprising a mixture of water, a gas such as air, and optionally a foaming agent, results in increased penetration rates, reduced bit wear and reduced reservoir damage due to erosion by the drilling fluid as compared with air. However, the water in the drilling fluid easily invades the reservoir necessitating large quantities of fluid for make up and also can cause plugging. It would be desirable to utilize a light-weight, gas-containing drilling fluid requiring less make up and causing less damage to the reservoir due to invasion thereof as well as having improved ability to remove cuttings from the hole.
U.S. Pat. application Ser. No. 639,652 filed Dec. 11, 1975 by Fischer et al. describes a gas-containing aqueous drilling fluid for drilling subterranean reservoirs containing a geothermal fluid, which drilling fluid contains lignite as a fluid loss control additive and a salt of a high molecular weight acrylic polymer as an additive to improve wall-building and cuttings-carrying properties. While this drilling fluid has been successful in some applications, scale-forming problems can arise when drilling through reservoirs whose high temperature aqueous liquids contain scale-forming ions.
U.S. Pat. No. 3,958,635 issued May 26, 1976 to Zilch et al. describes certain substituted iminodi(methylene phosphonic acid) compounds and water-soluble salts thereof useful as scale inhibitor additives for aqueous solutions containing scale-forming ions at temperatures of 400.degree. F. and above during production and utilization of such aqueous solutions.
U.S. Pat. application Ser. No. 625,814 filed Oct. 28, 1975 by Zilch et al. discloses certain amines, amides, thioamides, carboxylic acids or amide reaction products of carboxylic acids and various amines as scale inhibitor additives for the same use as discussed above.
Accordingly, a principal object of this invention is to provide a composition and method for inhibiting the formation of scale during the drilling of reservoirs containing high temperature aqueous solutions containing scale-forming ions, such as brines from oil and gas producing wells and geothermal fluids.
Another object of the invention is to provide such a composition and method for inhibiting the formation of a calcium-containing scale onto the face of the reservoir and the metal surfaces of well-drilling equipment coming in contact with such high temperature aqueous solutions.
A further object of the invention is to provide such a composition and method for inhibiting the formation of scale from liquid-containing geothermal fluids having temperatures above about 400.degree. F.
A still further object of the invention is to provide a light-weight drilling fluid and method of use thereof for drilling a subterranean reservoir containing a geothermal fluid.
Other objects, advantages and features of the invention will become apparent from the following description and appended claims.